At least one person was killed in the accident.
The boat was carrying 35 passengers, all tourists, and four crew members from Bali to the Gili islands when the engine reportedly blew up.
A woman died from head injuries, but at the time of going to press her nationality had yet to be confirmed.
Early information from Balinese authorities indicated some 14 tourists from countries including Germany, the UK, Australia and South Korea were injured in the incident, but did not elaborate on the severity of the injuries.
Portuguese government officials later confirmed neither of the Portuguese nationals was injured in the explosion.
Hours after the incident, a Government source told Lusa News Agency the Portuguese couple was “well” and were on their way back to Bali.
The explosion reportedly happened shortly after the boat set sail.